Transformers are used as elements of energy supply networks, for example for measuring electrical variables of high potentials, for network protection or for voltage conversion, for example for converting voltage from a first value at a high-voltage side to a second value that is smaller than the first value at a low-voltage side.
To measure the transfer behavior, for example to ensure the operational safety, or for other reasons, the determination of a plurality of characteristic magnitudes of the transformer by means of a measuring device can be necessary. Examples for such characteristic magnitudes include the determination of a winding resistance, the determination of a transformation ratio and/or the determination of a stray impedance or stray inductance of the transformer. In particular, the determination of the plurality of characteristic magnitudes comprises a plurality of individual measurements, in each of which an electrical voltage and/or an electrical current is registered and evaluated. Conclusions can, for example, be drawn from the measured characteristic magnitudes regarding the measurement accuracy (measurement or protection class) of the transformer.
An exemplary method with which different parameters of voltage converters can be determined is described in EP 2787 357 A2. The transfer accuracy of voltage converters can be determined on the basis of these parameters. A high accuracy and reproducibility in the determination of the parameters is necessary for the application of this method.
As a rule, the external circuitry (wiring configuration) of the transformer to be tested varies over the plurality of individual measurements, and this applies in particular when a so-called four-wire or four-conductor measurement method is used. A manual rewiring here can entail a high work effort and time expenditure, and lead to inaccurate or non-reproducible individual measurements. This also applies in particular to the creation of short circuits on the primary side or secondary side of the particular test object, where, depending on the test method applied at the time, such short circuits are often necessary.